Transient electronic device with ion-exchanged glass treated interposer

ABSTRACT

A transient electronic device utilizes a glass-based interposer that is treated using ion-exchange processing to increase its fragility, and includes a trigger device operably mounted on a surface thereof. An integrated circuit (IC) die is then bonded to the interposer, and the interposer is mounted to a package structure where it serves, under normal operating conditions, to operably connect the IC die to the package I/O pins/balls. During a transient event (e.g., when unauthorized tampering is detected), a trigger signal is transmitted to the trigger device, causing the trigger device to generate an initial fracture force that is applied onto the glass-based interposer substrate. The interposer is configured such that the initial fracture force propagates through the glass-based interposer substrate with sufficient energy to both entirely powderize the interposer, and to transfer to the IC die, whereby the IC die also powderizes (i.e., visually disappears).

RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 15/689,566, filedAug. 27, 2017, which is as divisional of U.S. Ser. No. 14/694,132, filedApr. 23, 2015, now U.S. Pat. No. 9,780,044.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention is based upon work supported by DARPA under Contract No.HR0011-14-C-0013 (3765). Therefore, the Government has certain rights tothis invention.

FIELD OF THE INVENTION

This invention relates to transient electronics, and in particular tointerposers utilized in transient electronic assemblies.

BACKGROUND OF THE INVENTION

Large area sensing is critical for a variety of military, ecological andcommercial interests and has historically been served through the use ofcentralized long-range sensors. However, rapid improvements inminiaturization of electronic systems have significantly improved thecapabilities of small sensor devices. These micro-sensors have thepotential to create “large N” distributed networks with advantages inoperational adaptability, non-traditional sensing modalities that areonly possible with close proximity, increased sensitivity and knowledgeextraction through networked intelligence.

While distributed network systems have remarkable promise, theirrealistic use is limited by risks associated with their accumulation inthe environment, detection and defeat, and exploitation due to inabilityto maintain positive control (unlike centralized long-range sensors).

The phrase “transient electronics” refers to a relatively new family ofelectronic devices that disappear (disaggregate and disperse) within aset period of time, making them ideally suited for distributed networksystems. Conventional transient electronic systems typically rely on theuse of soluble substrates and electronic materials (such as silk). Whenplaced into solvent (typically water), these conventional substrates andelectronics slowly dissolve into solution. As such, a distributednetwork system made up of conventional transient electronic devices canbe expected to “disappear” over a relatively short amount of time (e.g.,after periodic rainfall).

Although the conventional transient electronic approaches achieve thegoal of causing the electronics to “disappear” after use, the longdissolution period required to achieve complete disaggregation anddispersal make the conventional approaches unfit for discrete (e.g.,military) applications that require rapid and complete disaggregationupon command. Moreover, the conventional approaches utilize materialsthat are not compatible with existing integrated circuit fabrication andassembly techniques, requiring the development of new IC fabricationprocesses at significant cost.

Interposers are well-known electrical interfaces in the context ofsemiconductor device packaging, and are typically disposed between an ICdie (chip) and a standardized semiconductor package structure, such as aball-grid array (BGA) package or a pin-grid array (PGA) package.Interposers typically include a flat insulator substrate (e.g., either arigid insulator such as FR4, or a flexible insulator such as polyimide)through which multiple metal conductors extend between correspondingcontact structures (points) that are disposed in two different patternson opposing substrate surfaces. That is, a first set of contact pointsdisposed on one side of the interposer substrate are formed in a patternthat matches corresponding contact pads on the IC die to facilitateIC-to-interposer connection (e.g., by way of surface mountingtechniques), and a second set of contact points on the opposing side ofthe interposer are arranged in a second (different) pattern that matchescorresponding contact structures disposed on an inside surface of thehost package to facilitate surface mounting of the interposer to thehost package. The metal conductors pass through the interposer substrateto provide signal paths between corresponding contact structures of thefirst and second sets. With this arrangement, when the host packagestructure is subsequently connected, e.g., to the printed circuit board(PCB) of an electrical system, the interposer facilitates passingsignals between the IC die(s) and the electrical system by way of theI/O pins/balls of the host package.

Interposers were originally typically utilized to reroute IC dieconnections to corresponding contact points on standard packagestructures, but more recently serve other purposes as well. For example,as advances in semiconductor fabrication facilitate smaller IC diehaving correspondingly finer pitched IC die contact pads, interposersare also utilized to spread the finely spaced IC die contact points towider pitches that are more compatible with conventional packagestructures. In this case, the interposer includes first contact pointsarranged in a finely pitched (first) pattern on one surface, and secondcontact points arranged in a widely pitched (second) pattern on theopposing surface, with conductive metal vias and traces extendingthrough the substrate and along the opposing surfaces to provideelectrical signal paths between associated first and second contactpoints. In addition to spreading finely spaced IC die contact points towider pitches, interposers are being used to secure two or more die intoa single package structure.

What is needed is a transient electronic package assembly that iscompatible with existing IC fabrication techniques, and achievessufficiently complete, on-command disaggregation of IC die disposedthereon to provide both security and anti-tampering protection by way ofpreventing access to the intact integrated circuit implemented on the ICdie.

SUMMARY OF THE INVENTION

The present invention is directed to a transient electronic device inwhich at least one integrated circuit (IC) die is mounted in a packagestructure by way of an intervening glass-based interposer, where theinterposer includes a glass substrate that is treated to contain asufficient amount of ions such that it fractures (powderizes) inresponse to a transient event triggering signal, and in doing so to alsofractures (powderizes) the IC die(s) bonded thereon. Similar toconventional arrangements, the novel interposer includes a first set ofcontact points (i.e., metal pads or other contact structures) disposedon a first substrate surface and arranged in a (first) pattern thatmatches corresponding contact pads of the IC die, a second set ofcontact points disposed on the opposing substrate surface and arrangedin a (second) pattern that matches corresponding contact structures of apackage structure, and conductors extending on and/or through thesubstrate that form electrical signal paths between associated first andsecond contact points. According to an aspect of the invention, the ICdie is fixedly attached to the interposer, and the interposer includes aglass substrate that is rendered fragile by way of ion-exchangetreatment such that an initial fracture force generated by a triggerdevice in response to a trigger signal propagates through the interposerand powderizes the IC die. Specifically, the ion-exchange treated glasssubstrate is treated using known ion-exchange processes such that theglass is rendered with enough stored energy to generate secondaryfractures in response to the initial fracture force such that thesecondary fractures propagate throughout the glass substrate, wherebythe glass substrate completely disaggregates (“powderizes”) intomicron-sized particulates (i.e., ≤100 μm across) using a mechanismsimilar to that captured in a Prince Rupert's Drop. By fixedly attachingthe IC die to the glass substrate utilizing a suitable conventionalbonding technique (e.g., anodic bonding or by way of sealing glass), thesecondary fractures also propagate into the IC die with sufficientenergy to powderize the IC die (i.e., substantially simultaneously withthe powderization of the interposer substrate). The present inventionthus facilitates the production of transient electronic devices andsystems in which functional circuitry formed on the IC die(s)effectively disappears (powderizes) in a significantly shorter amount oftime than is possible using conventional (e.g., soluble substrate)approaches. Moreover, by configuring the trigger device to initiatepowderization upon detecting unauthorized tapering (e.g., tampering withthe package structure or a printed circuit board to which the transientdevice is mounted), the present invention provides both security andanti-tampering protection by preventing unauthorized access to theintegrated circuit implemented on the IC die while it is intact.Further, because the interposer is compatible with low-cost existing ICfabrication techniques, the present invention facilitates the productionof transient electronic systems including electronic devices withminimal (or potentially without any) modification to core IC fabricationprocess.

According to an embodiment of the present invention, the interposer'sglass substrate comprises a thin glass wafer/sheet (e.g., having athickness in the range of 100 μm and 300 μm) of an ion-exchange specificglass (e.g., all silicate glasses having adequate alkali compositions)that is etched (e.g., using laser, mechanical or chemical etchingtechniques) to include multiple through-glass via (TGV) openings. TheTGV openings are then filled with a conductive material (e.g., a metalsuch as copper), where the conductive material preferably has aCoefficient of Thermal Expansion (CTE) that is matched to (i.e., +/−10%of) the CTE of the ion-exchange specific glass, whereby the conductivematerial forms metal via structures having opposing ends that areexposed on the opposing substrate surfaces. Contact points (e.g., metalpads) and optional metal trace structures are then respectivelypatterned on one or both of the opposing substrate surfaces, the contactpoints being arranged in the desired patterns mentioned above, and theoptional metal traces being patterned to provide electrical connectionsbetween corresponding pairs of upper/lower (first/second) contact pointsand opposing ends of associated metal via structures, thereby formingthe interposer conductor (conductive path) between the correspondingpairs of upper/lower (first/second) contact points.

According to a presently preferred embodiment, a transient event triggerdevice is fabricated or otherwise disposed on each interposer when theinterposer contact structures and metal trace structures are formed onthe glass substrate. The trigger device includes an actuating mechanismthat controls the release of (i.e., generates and applies) the initialfracture force in response to a trigger signal (e.g., an externallydelivered current pulse) that is supplied to the trigger device. Inalternative embodiments, the actuating mechanism comprises one of adevice configured to apply resistive heating to the glass substrate, anda device configured to apply a mechanical pressure to the glasssubstrate. By configuring the trigger device in this way, upon receivinga trigger signal, the actuating mechanism is able to generate and applya sufficiently strong initial fracture force to the glass substrate suchthat the interposer suddenly and catastrophically powderizes withsufficient force to assure complete destruction (powderization) of theIC die(s) mounted thereon.

According to another aspect of the invention, the IC die are fabricatedand fixedly attached to the glass substrate using fabrication and diebonding techniques that assure coincident powderization of the IC diewith the interposer. In a presently preferred embodiment, the IC dieincludes an IC device that is fabricated using standardsilicon-on-insulator (SOI) fabrication techniques (i.e., such that thefunctional circuitry is implemented as an SOI integrated circuitstructure). In one embodiment, the IC die is attached to the glasssubstrate using anodic bonding, which provides good interface adhesionfor allowing crack propagation from the glass substrate to assuredestruction of the adhered chip. In an alternative embodiment, anotherbonding method, such as using sealing glass, may be utilized. By formingthe functional circuitry as SOI integrated circuits and anodicallybonding the IC die to the glass substrate, reliable powderization of theIC die into small particulates during transient events is achieved. Inanother embodiment, the IC die is “thinned” (e.g., subjected to chemicalmechanical polishing) either before or after the bonding process toreduce a thickness of the IC die, which further assures powderization ofthe IC die during a transient event.

According to another embodiment of the present invention, a method forproducing transient electronic devices includes at least partiallyforming the interposer structure described above and subjecting theglass substrate to an ion-exchange treatment such that the frangibilityof the glass substrate is increased. An optional shallow ion-exchangeprocess is performed after the via etch to increase the frangibilityalong the via sidewalls. The trigger device (described above), theinterposer contact structures and metal trace structures areformed/disposed on the glass substrate either before or after theion-exchange treatment. One or more IC die are then fixedly attached(e.g., by anodic bonding) to an upper (first) surface of the treatedglass substrate such that IC contact points are electrically connectedto corresponding (first) interposer contact structures, and then theinterposer is mounted onto a package structure such that contactstructures disposed in a second pattern on the package structure areelectrically connected to corresponding (second) interposer contactstructures disposed on the lower (second) surface of the glasssubstrate. As described above, the interposer's glass substrate issubjected to ion-exchange treatment such that its ion content isincreased until the treated glass substrate is sufficiently fragile togenerate secondary fractures in response to the initial fracture forcesupplied by the trigger device, and the IC die is bonded to the treatedglass substrate such that the secondary fractures propagate into the ICdie with sufficient energy to powderize the IC die. The final particlesize after triggering is based upon factors such as the glass substratethickness, the level of ion-exchange processing, the die bonding processand the initial fracture force. In one embodiment, the IC die ispatterned to provide fracture points (features) that assist incontrolling the final fractured particle size (i.e., the fracturefeatures are formed such that, when the glass substrate is powderized,the IC chip fractures along the patterned fracture features).

According to alternative specific embodiments the transient electronicdevice manufacturing method involves either sheet level interposerpatterning or die level interposer patterning. In each case, multipleinterposer cores are integrally disposed on a single glass sheet (i.e.,the glass substrate of each interposer core is formed by a correspondingportion of the glass sheet). In the sheet level patterning approach,interposer contact structures and trigger devices are formed on eachinterposer core, then the glass sheet is diced to separate theindividual interposers, which are then subjected to ion-exchangetreatment (e.g., individually or in a batch), and then IC dies are thenbonded onto each of the interposers. According to the die levelpatterning approach, the glass sheet is diced to separate the individualinterposers and ion-exchange treatment is performed before interposercontact structures and trigger devices are formed on each interposercore, then IC dies are bonded onto each of the interposers. The maindifferences between these two approaches are cost and performance.Patterning the interposer layer before dicing will improve throughputand reduce cost but ion-exchanging the glass with patterned metal layerswill also create a non-uniform surface stress profile which may reducethe frangibility. On the other hand, ion-exchanging individual diebefore patterning will provide a more reliable frangible substrate butthe added cost of patterning individual pieces may not be favorable.Other variations to these exemplary approaches are evident to thoseskilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects and advantages of the presentinvention will become better understood with regard to the followingdescription, appended claims, and accompanying drawings, where:

FIG. 1 is a top side perspective view showing a transient electronicdevice produced in accordance with an exemplary embodiment of thepresent invention;

FIG. 2 is a flow diagram showing a generalized manufacturing process forproducing the transient electronic device of FIG. 1;

FIG. 3 is a flow diagram showing a manufacturing process for producingan interposer core including through-glass metal via structure accordingto an embodiment of the present invention;

FIGS. 3(A), 3(B), 3(C), 3(D) and 3(E) are simplified cross-sectionalside views showing the production of an interposer core according to theprocess flow of FIG. 3;

FIGS. 4(A), 4(B), 4(C), 4(D) and 4(E) are simplified cross-sectionalside views showing the production of a multiple transient electronicdevices according to a sheet level patterning embodiment of the presentinvention;

FIGS. 5(A), 5(B), 5(C), 5(D) and 5(E) are simplified cross-sectionalside views showing the production of a multiple transient electronicdevices according to a die level patterning embodiment of the presentinvention;

FIGS. 6(A), 6(B), 6(C), 6(D), 6(E) and 6(F) are cross-sectional sideviews showing a transient electronic device produced in accordance withanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention relates to an improvement in transient electronicdevices. The following description is presented to enable one ofordinary skill in the art to make and use the invention as provided inthe context of a particular application and its requirements. As usedherein, directional terms such as “upper”, “upward”, “lower”,“downward”, are intended to provide relative positions for purposes ofdescription, and are not intended to designate an absolute frame ofreference. Various modifications to the preferred embodiment will beapparent to those with skill in the art, and the general principlesdefined herein may be applied to other embodiments. Therefore, thepresent invention is not intended to be limited to the particularembodiments shown and described, but is to be accorded the widest scopeconsistent with the principles and novel features herein disclosed.

FIG. 1 is a simplified diagram including perspective and cross-sectionalviews showing a transient electronic device 100 in a pre-transience“whole” state (i.e., device 100(t 0) shown in the middle and upperportions of FIG. 1) and a post-transience “powderized” state (i.e.,device 100(t 1) shown in the lower portion of FIG. 1).

Referring to the middle and upper portions of FIG. 1, in thepre-transience state (e.g., immediately after production), transientelectronic device 100(t 0) generally includes an integrated circuit (IC)die 120 and a trigger device 130 that are disposed on an interposer 110,with interposer 110 mounted onto an exemplary package structure 140.

Referring to the bubble located in the upper right portion of FIG. 1, ICdie 120 is an integrated circuit device including an electronic circuit122 formed on a substrate 121 (i.e., e.g., a semiconductor “chip”) usingany know semiconductor fabrication technique, although in a presentlypreferred embodiment, IC die 120 is silicon-on-insulator (SOI)integrated circuit device. Electronic circuit 122 includes one or moreelectronic elements that are configured to perform a prescribed usefulfunction (e.g., sensor operations) up until a transient event, asdescribed below. IC contact pads 125 are disposed in a first pattern P1on a surface of the semiconductor substrate 121 and are operably coupledto electronic circuit 122, e.g., by way of conventional metallizationpatterns (not shown).

As depicted in the upper left portion of FIG. 1, package structure 140is depicted in the exemplary embodiment as a ball-grid array (BGA)package structure including multiple balls or bumps 146 configured tofacilitate surface-mount assembly onto a system circuit board (notshown). Specifically, as indicated the bubble located in the upper rightportion of FIG. 1, package 140 includes multiple (first) package contactstructures 145 disposed in a second pattern P2 on an upper surface 142of a package substrate 141, with balls/bumps (second package contactstructures) 146 disposed on and extending from a lower surface 143 ofsubstrate 141. Package conductors 147 are formed using known techniquesand extend through package structure 141 to provide signal paths betweenassociated contact structures (e.g., conductor 147-1 forms an electricalpath between package contact structure 145-1 and associated ball/bump146-1). Of course, package structure 140 may be implemented using otherpackage types, such as pin-grid array package structures.

Referring again to the upper left portion of FIG. 1, similar toconventional arrangements, interposer 110 is disposed between IC die 120and package structure 140, and is secured to package substrate 140 suchthat it serves as an adapter that couples each contact pad 125 of IC die120 to a corresponding ball/bump 146 on package structure 140.Specifically, interposer 110 includes a thin glass substrate 111 havingan upper surface 112 and an opposing lower surface 113 separated by asubstrate thickness T_(GLASS) that, in a presently preferred embodiment,is in the range of 100 μm and 300 μm. A first set of contact points(i.e., metal pads or other contact structures) 115 are disposed inpattern P1 on upper surface 112 such that the position of each contactpoint 115 matches the location of a corresponding contact pad 125 of theIC die 120 to facilitate operable electrical connection (e.g., by way ofsolder structures 150) when IC die is surface mounted and fixedlyattached (e.g., bonded) onto interposer 110. For example, as indicatedin the bubble in FIG. 1, contact point 115-1 is aligned withcorresponding contact pad 125-1, and is electrically connected by way ofsolder structure 150-1. Interposer 110 is secured to package substrate140 by way of second contact points 116 disposed on lower surface 113,which are arranged in pattern P2 and respectively electrically connected(e.g., by way of solder structures 155) to corresponding package contactstructures 145 on package structure 140 to facilitate operableelectrical connection when interposer 110 is operably mounted ontopackage structure 140. For example, as indicated in the bubble in FIG.1, contact point 116-1 is aligned with corresponding contact structure145-1, and is electrically connected by way of solder structure 155-1.Interposer 110 further includes multiple conductors that form electricalsignal paths between associated contact points 115 and 116, where eachconductor includes a metal via structure 117 disposed in an associatedthrough-glass via (TGV) opening 114 that extends through glass substrate111, and one or more optional metal traces 118 that are formed on one ormore of upper surface 112 and lower surface 113. For example, contactpoints 115-1 and 116-1 are connected by a conductor formed by metal viastructure 117-1 and metal trace 118-1, which is formed on lower surface113. Accordingly, interposer 110 provides an electrical signal pathbetween contact pad 125-1 of IC die 120 and ball/bump 146-1 of packagestructure 140 by way of contact point 116-1, which is connected toball/bump 146-1 by contact structure 145-1 and conductor 147-1, theconductor formed by metal via structure 117-1 and metal tract 118-1, andcontact point 115-1.

As described in additional detail below, trigger device 130 functions toinitiate powderization (fragmentation) of IC die 120 during a transientevent by way of generating and applying an initial fracture force ontoglass substrate 111 in response to an externally generated triggersignal TS. Specifically, trigger device 130 is configured to generate aninitial fracture force in response to externally generated triggersignal TS, and is operably attached to upper surface 112 of glasssubstrate 111 such that the generated initial fracture force is appliedonto glass substrate 111. As explained below, the initial facture forceis generated with sufficient energy to cause powderization of interposer110 and IC die 120.

According to an aspect of the invention, glass substrate 111 comprisesan ion-exchange specific glass material (i.e., a glass that is receptiveto ion exchange treatment), and interposer 110 is fabricated usingprocesses that render glass substrate 111 sufficiently fragile suchthat, in response to the initial fracture force generated by triggerdevice 130, secondary fractures are generated and propagate throughglass substrate 111 with sufficient energy to powderize glass substrate111. Specifically, after an interposer core is generated in the mannerdescribed below, glass substrate 111 is subjected to treatment(tempering) using known ion-exchange processes such that the ioniccontent of glass substrate 111 (i.e., the amount of ions contained inglass substrate 111) is increased to a point that renders the glasssufficiently fragile such that, during a subsequent transient event,secondary fractures are generated in glass substrate 111 in response tothe initial fracture force applied by trigger device 130. Further, asindicated by device 100(t 1) at the lower portion of FIG. 1, glasssubstrate 111 is rendered sufficiently fragile by the ion-exchangetreatment such that the secondary fractures propagate throughout glasssubstrate 111 during a transient event, whereby the glass substrate 111completely disaggregates (“powderizes”) into micron-sized particulates(i.e., ≤100 μm across) using a mechanism similar to that captured in aPrince Rupert's Drop. That is, as indicated in the bubble located at thelower left portion of FIG. 1, the secondary fractures travel rapidlythroughout treated glass substrate 111, whereby glass substrate 111 issuddenly and catastrophically disaggregated (powderized) intomicron-sized particulates 101 (i.e., having length L, width W, andheight H dimensions that are less than approximately 100 μm across). Theoptimal ion content of glass substrate 111 needed to achieve theabove-described state of fragility (i.e., the parameters of theion-exchange processing to which the interposer core is subjected) isdependent on several factors including the type and thickness of glasssubstrate 111, and determining the optimal amount is within thecapabilities of those skilled in the art.

According to another aspect of the invention, IC die 120 is fixedlyattached to interposer 110 such that the secondary fractures generatedin glass substrate 111 during a transient event are transmitted withsufficient force to also powderize IC die 120. By fixedly attaching ICdie 110 to glass substrate 111 utilizing a suitable conventional bondingtechnique (e.g., anodic bonding or by way of sealing glass), thesecondary fractures generated in glass substrate 111 also propagate intoIC die 120 with sufficient energy to powderize IC die 120 (i.e.,substantially simultaneously with the powderization of interposer 110,as depicted at the bottom of FIG. 1). The present invention thusfacilitates the production of transient electronic device 100 in whichfunctional circuitry formed on IC die 120 effectively disappears(powderizes) in a significantly shorter amount of time than is possibleusing conventional (e.g., soluble substrate) approaches. Moreover, byconfiguring trigger device 130 to initiate powderization upon detectingunauthorized tapering (e.g., tampering with package structure 140 or asystem circuit board, not shown, to which transient device 100 ismounted), the present invention provides both security andanti-tampering protection by preventing unauthorized access toelectronic circuit 122 while IC die 120 is intact. Further, becauseinterposer 110 is compatible with low-cost existing IC fabricationtechniques, the present invention facilitates the production oftransient electronic device 100 with minimal (or potentially withoutany) modification to the core IC fabrication processes.

FIG. 2 is a flow diagram showing a manufacturing process for producingtransient electronic device 100 (see FIG. 1) according to an exemplaryembodiment, where the method generally includes subjecting interposer110 to ion-exchange treatment, then fixedly attaching IC die 120 totreated glass substrate 111, then securing interposer 110 to package140. Referring to block 210 at the upper portion of FIG. 2, the methodbegins by procuring or fabricating an interposer core (e.g., a suitableglass substrate including metal via structures, but not includingcontact structures, metal traces or a trigger device). Fabrication of anexemplary interposer core is described below with reference to FIGS. 3and 3(A) to 3(E). Next, ion-exchange treatment is performed to increasethe ionic content of the glass substrate (block 220), and fabrication ofthe interposer is completed (i.e., contact structures are formed inaccordance with predetermined arrangements, such as patterns P1 and P2described above with reference to FIG. 1, metal traces are formed on oneor both substrate surfaces, and a trigger device is formed or mounted onthe glass substrate). As indicated by arrow A in FIG. 2 and as set forthin the specific exemplary embodiments described below, either theunfinished interposer core is subjected to ion-exchange treatment inblock 220, or the interposer is finished in block 230 and then subjectedto ion-exchange treatment in block 220. As indicated in block 240, afterion-exchange treatment is performed, one or more IC die(s) is/are bondedto each interposer in the manner described above using die-bondingtechniques that promote the the propagation of secondary fractures fromthe interposer into the IC die(s) during transient events withsufficient energy to powderize the IC die(s). Referring to block 250,the interposer is then operably secured onto a package structure (e.g.,BGA package structure 140, shown in FIG. 1), whereby the transientelectronic device is ready for assembly into a host system.

FIG. 3 is a flow diagram showing a manufacturing process for producingan interposer core according to an embodiment of the present invention,and FIGS. 3(A) to 3(E) depict an exemplary interposer core duringvarious stages of process flow of FIG. 3.

Referring to block 211 in FIG. 3 and to FIG. 3(A), the process begins byprocuring an ion-exchange specific glass sheet 111A having a suitablethickness T_(GLASS). Suitable ion-exchange specific glass includesunstrengthened Corning Gorilla Glass, SCHOTT Xensation and AGCDragontrail glass, which are available from from various glassdistributors such as Abrisa Technologies in Santa Paula, Calif.

Referring to block 213 in FIG. 3 and to FIG. 3(B), through-glass via(TGV) openings 114A are formed that extend entirely through glasssubstrate 111A (i.e., between upper surface 112A and lower surface113A). In alternative specific embodiments, TGV openings 114A are byetching or otherwise ablating portions of glass substrate 111A using oneof a laser etching process, a mechanical etching process and a chemicaletching process (which are collectively indicated by arrows 310 in FIG.3(B).

Referring to block 215 in FIG. 3 and to FIG. 31, an optional shallowion-exchange process (indicated by arrows 320) is then performed (i.e.,before forming metal via structures in TGV openings 114).

Metal via structure 117A are then formed in each TGV openings 114A usinga suitable method. Referring to block 217 in FIG. 3 and to FIG. 3(D), inone specific embodiment a metal material 330 is deposited over uppersurface 112A and lower surface 113A such that portions of the metalmaterial enter each TGV opening 114A and forms corresponding metal viastructures 117A. Referring to block 219 in FIG. 3 and to FIG. 3(E),residual portions of the metal material are then removed from uppersurface 112A and lower surface 113A, e.g., using a suitable etchant 340.As depicted in FIG. 3(E), the etching process is performed such thatresulting interposer core 110A includes each metal via structure 117Aextends through glass substrate 111A and has opposing ends that arerespectively exposed on upper surface 112A and lower surface 113A, whichfacilitates connection to subsequently formed structures (e.g.,interposer contact structures and metal trace structures).

The interposer cores described above are then processed to providecompleted interposers onto which IC dies are mounted. According toalternative exemplary embodiments, interposer cores are processed usingeither sheet level patterning or die level patterning. An exemplarysheet level patterning process is described below with reference toFIGS. 4(A) to 4(E), and an exemplary die level patterning process isdescribed below with reference to FIGS. 5(A) to 5(E). Both sheet leveland die level processing begin with multiple interposer cores that areformed and integrally connected together on a single glass sheet. Forexample, as shown in FIG. 4(A), a single (continuous/unbroken) glasssheet 111B includes three integrally connected interposer cores 110B-1,110B-2 and 110B-3, each having a respective glass substrate 111B-1111B-2 and 111B-3 formed by a corresponding portion of glass sheet 111B.Similarly, as shown in FIG. 5(A), integral interposer cores 110C-1,110C-2 and 110C-3 have respective glass substrates 111C-1 111C-2 and111C-3 formed by corresponding portions of a single glass sheet 111C.

Starting with the integral interposer cores shown in FIG. 4(A), sheetlevel patterning begins as shown in FIG. 4(B) by patterning contactstructures, optional metal trace structures, and trigger devices ontoeach interposer core using known techniques. For example, contactstructures 115 (and optional metal trace structures, not shown) areformed of glass sheet 111B by way of printing a suitable metal 350B ontoupper sheet surface 112B. Contact structures 116 and optional metaltrace structures (not shown) are formed on lower sheet surface 113B arethen formed, for example, by inverting sheet 111B and repeating themetal printing process. Trigger devices 130B-1 to 130B-3 are then formedby depositing a suitable material 360B using a printing process, or bysurface mounting a pre-formed structure onto each interposer 110B-1 to110B-3, respectively. Referring to FIG. 4(C), glass sheet 111B is thendiced (e.g., cut using a laser 370B) to separate interposers 110B-1 to110B-3 from each other, and then the individual interposers 110B-1 to110B-3 are subjected to ion-exchange treatment (indicated by arrows380B) as shown in FIG. 4(D). As indicated in FIG. 4(E), afterion-exchange treatment, IC dies 120B-1, 120B-2 and 120B-3 are thenbonded onto interposers 110B-1, 110B-2 and 110B-3, respectively.

Die level patterning, which is depicted in FIGS. 5(A) to 5(E), involvesprocessing each interposer core separately. That is, starting with theintegral interposer cores shown in FIG. 5(A), die level patterningbegins with dicing (e.g., cutting using a laser 370C) to separateinterposer cores 110C-1 to 110C-3 from each other, then the individualinterposer cores 110C-1 to 110C-3 are subjected to ion-exchangetreatment (indicated by arrows 380C), as shown in FIG. 5(C). Afterion-exchange treatment, as shown in FIG. 5(D), contact structures 115and 116, optional metal trace structures, and trigger devices 130C-1 to130C-3 are formed on each interposer core 110C-1 to 110C-3 using thetechniques mentioned above, and then, as indicated in FIG. 5(E), IC dies120C-1, 120C-2 and 120C-3 are then bonded onto interposers 110C-1,110C-2 and 110C-3, respectively.

FIGS. 6(A) to 6(F) depict the fabrication and subsequent actuation of atransient electronic device 100D according to another embodiment of thepresent invention.

FIG. 6(A) depicts an interposer 110D produced in a manner consistentwith the methodologies mentioned above. For descriptive purposes,associated contact structures 115D and 116D, which are respectivelydisposed on upper surface 112D and lower surface 113D, are connected byway of simple contact structures comprising an associated metal viastructure 117D. In the present embodiment, trigger device 130D iselectrically controlled, and more specifically utilizes a heatingelement to generate local heating in response to an applied electricalpulse transmitted through metal via structures 137D, which are connectedto associated contact structures 136D disposed on lower surface 113D. Inone embodiment, trigger device 130D is constructed by forming awide/thicker lower resistance electrodes 132D onto associated upper endportions of metal via structures 137D, and then forming a resistive,thin, narrow resistor (actuator) structure 135D between electrodes 132D,where resistor structure 135D is formed using a material that is capableof sustaining high temperature (e.g., a metal such as tungsten). Triggerdevice 130D is fabricated directly onto glass substrate 110D usingstandard microfabrication techniques (vapor deposition andphoto-patterning) or simply through shadow-masked evaporation.

FIG. 6(B) depicts the subsequent fixed attachment of IC die 120D toglass substrate 111D by way of either sealing glass 127D or an anodicbond. As described above with reference to FIG. 1, IC die 120D ismounted such that contact pads 125D make electrical contact with contactstructures 115D disposed on upper surface 112D of glass substrate 111D.

FIG. 6I depicts securing interposer 110D to a package structure 140D inorder to complete the assembly of transient electronic device 110D. Asset forth above, interposer 110D is mounted such that package contactstructures 145D-1 are electrically connected to corresponding interposercontact structures 116D, which are disposed on lower surface 113D ofglass substrate 111D. In this embodiment, the actuation of triggerdevice 130D is also enabled by way of electrical connection betweenpackage contact structures 145D-2 and corresponding contact structures136D, which forms a signal path between balls/bumps 146D of packagestructure 140D and trigger device 130D by way of conductors (not shown)formed in package structure 140 and metal via structures 137D disposedin interposer 110D.

As also depicted in FIG. 6I, in one embodiment IC die 120D is thinnedvia chemical mechanical polishing (CMP) 390D to a realistic thicknessT_(DIE) in order to further promote powderization. The key to achievingfragmentation of IC die 120D is coupling the propagating fracture cracksfrom glass substrate 111D into IC die 120D, which is further enabled bythinning IC die 120D (i.e., either after attachment to interposer 110D,as depicted, or before attachment). The fragmentation process can beviewed as a competition between two possible outcomes: a crack canpropagate upward into the die substrate/silicon, or make a sharp turnand instead propagate through the bond region, leading to de-bonding. Toexceed the ratio needed for a glass/silicon bond, either an anodic bondor a low-melting-point sealing glass 127D is utilized to secure IC die120D to glass substrate 111D. Alternatively, eutectic or adhesivebonding may be used to secure IC die 120D to glass substrate 110D.

FIG. 6(D) depicts the subsequent attachment of transient electronicdevice 100D to a system level printed circuit board 160D, which suppliespower to and communicates with IC 120D by way of package structure 140Dand interposer 110D. In the exemplary embodiment, circuit board 160D ismounted inside a secured housing (not shown) that includes a securitysystem (e.g., sensors) capable of detecting unauthorized tampering withthe housing, and a control system configured to communicate with IC die120D and trigger device 130D. That is, under normal operatingconditions, the system controller facilitates functional operation of ICdie. However, as described below with reference to FIGS. 6(E) and 6(F),when the system controller detects unauthorized tampering with thesystem housing (which may be related to an attempt to access or tamperwith the functional circuitry of IC die 120D), the system controllertransmits trigger signals to trigger device 130D in order to initiate atransient event.

FIGS. 6(E) and 6(F) illustrate the controlled destruction(disaggregation) of transient electronic device 100D during a transientevent (i.e. in response to a trigger signal TS applied to transientelectronic device 100D by way of balls/bumps 146D of package structure140D). In the exemplary embodiment, the mechanism of fracture generatedby trigger device 130D is hoop stress generated as the portion of glasssubstrate 110D heated by resistor structure 135D expands. Simulation ofsuch trigger devices indicate that 0.5 ms after the current pulse isapplied, tensile hoop stresses in the range of 100-150 Mpa are presentbelow the resistor structure—this would be sufficient to initiatefracture in almost any traditionally tempered glass. These simulationresults show that large surface tensile stresses can be obtained with amodest amount of current and energy. In this example, based onresistance estimates using properties for tungsten, the current isapproximately 70 mA, and the voltage developed across the resistor isabout 80 mV. These amounts are well within the capabilities of currentlyavailable small-form-factor batteries. As indicated in FIG. 6(E), attime t0 (i.e., immediately after transmission of trigger signal TS), aresulting initial fracture F₀ is generated in glass substrate 110D byway of localized heating, but IC die 120D remains entirely intact. Asindicated in FIG. 6(F), secondary fractures F_(P) are generated in glasssubstrate 111D(t1) in response to the initial fracture force thatpropagate throughout glass substrate 111D(t1), whereby said glasssubstrate 111D(t1) is powderized into particulates 101D. In addition,because IC die 120D(t1) is sufficiently bonded to glass substrate111D(t1), secondary fractures F_(P) propagate into IC die 120D(t1) withsufficient energy to powderize the die material into particulates 101D.

In addition to the localized heating approach described in the previousembodiment, other trigger devices may be utilized to generate theinitial fracture required to generate powderization of the device. Forexample, suitable trigger devices may be produced that generatelocalized fracturing using by initiating a chemical reaction on thesurface of the glass substrate, or by applying a localized mechanicalpressure (e.g., using a piezoelectric element) on the glass substrate.

Although the present invention has been described with respect tocertain specific embodiments, it will be clear to those skilled in theart that the inventive features of the present invention are applicableto other embodiments as well, all of which are intended to fall withinthe scope of the present invention.

The invention claimed is:
 1. A transient device comprising: anintegrated circuit (IC) die including a semiconductor substrate havingan electronic circuit formed thereon, and IC contact pads disposed in afirst pattern on a surface of the semiconductor substrate, the ICcontact pads being operably coupled to the electronic circuit; a packagestructure including a package substrate, a plurality of first packagecontact structures disposed in a second pattern on a first surfacethereof, a plurality of second package contact structures disposed on asecond surface thereof, and a plurality of package conductors extendingthrough the package structure between the first and second surfaces suchthat each package conductor forms an electrical path between anassociated first package contact structure and an associated secondpackage contact structure; an interposer comprising a glass substrateincluding a plurality of first contact points disposed in the firstpattern on a first surface thereof, a plurality of second contact pointsdisposed on a second surface thereof, and a plurality of interposerconductors, each interposer conductor being configured to form anelectrical path between an associated first contact point and anassociated second contact point; and a trigger device attached to theinterposer and configured to generate and apply an initial fractureforce on the glass substrate in response to a trigger signal, whereinthe interposer is secured to the package substrate such that each of thesecond contact points disposed on the second surface are electricallyconnected to corresponding first package contact structures, wherein theglass substrate is configured such that secondary fractures aregenerated in the glass substrate in response to the initial fractureforce and propagate through the glass substrate, and wherein the IC dieis fixedly attached to the glass substrate such that the secondaryfractures propagate into the IC die with sufficient energy to fracturethe IC die.
 2. The device of claim 1, wherein the glass substratecomprises a thickness in the range of 100 μm and 300 μm.
 3. The deviceof claim 2, wherein the glass substrate comprises a silicate glass. 4.The device of claim 2, wherein the glass substrate defines a pluralityof through-glass vias extending between the first surface and the secondsurface thereof.
 5. The device of claim 4, wherein each the interposerconductor comprises a metal via structure extending through anassociated through-glass via.
 6. The device of claim 5, wherein themetal via structure comprises a conductive material having a Coefficientof Thermal Expansion (CTE) that is matched to a CTE of the glasssubstrate.
 7. The device of claim 4, wherein at least some of theinterposer conductors further comprises a metal trace structure disposedon one of the first surface and the second surface and extending from anassociated metal via structure to one of an associated first contactpoint and an associated second contact point.
 8. The device of claim 1,wherein the trigger device comprises an actuating mechanism configuredto control release of the initial fracture force in response to anexternally supplied trigger signal.
 9. The device of claim 8, whereinthe actuating mechanism comprises one of a device configured to applyresistive heating to the glass substrate and a device configured toapply a mechanical pressure to the glass substrate.
 10. The device ofclaim 1, wherein the IC die is anodically bonded to the glass substrate.11. The device of claim 1, wherein the IC die comprises asilicon-on-insulator (SOI) integrated circuit device.
 12. The device ofclaim 1, further comprising one or more sensors configured to detect atampering event; and a controller communicatively coupled to the triggerdevice and configured to trigger the trigger device in response todetection of the tampering event.
 13. The device of claim 12, whereinthe controller is communicatively coupled to the IC.
 14. The device ofclaim 12, further comprising a housing and wherein the sensors areconfigured to detect tampering with the housing.
 15. A method,comprising: providing a trigger signal to a trigger device attached toan interposer of a transient device, the transient device including: thetrigger device; an integrated circuit (IC) die including a semiconductorsubstrate having an electronic circuit formed thereon, and IC contactpads disposed in a first pattern on a surface of the semiconductorsubstrate, the IC contact pads being operably coupled to the electroniccircuit; a package structure including a package substrate, a pluralityof first package contact structures disposed in a second pattern on afirst surface thereof, a plurality of second package contact structuresdisposed on a second surface thereof, and a plurality of packageconductors extending through the package structure between the first andsecond surfaces such that each package conductor forms an electricalpath between an associated first package contact structure and anassociated second package contact structure; an interposer comprising aglass substrate including a plurality of first contact points disposedin the first pattern on a first surface thereof, a plurality of secondcontact points disposed on a second surface thereof, and a plurality ofinterposer conductors, each interposer conductor being configured toform an electrical path between an associated first contact point and anassociated second contact point; in response to the trigger signal, thetrigger device generating and applying an initial fracture force on theglass substrate; the initial fracture force generating secondaryfractures in the glass substrate that propagate through the glasssubstrate and into the IC die; and the IC die fracturing in response tothe secondary fractures.
 16. The method of claim 15, further comprising:sensing a tampering event; and wherein providing the trigger signalcomprises generating the trigger signal in response to sensing thetampering event.
 17. The method of claim 15, wherein generating andapplying the initial fracture force comprises applying resistive heatingto the glass substrate.
 18. The method of claim 15, wherein generatingand applying the initial fracture force comprises applying mechanicalpressure to the glass substrate.